The present invention relates to a splittable multi-component fiber of good splittability, a method for producing it, and a fibrous article comprising it. More precisely, the invention relates to a splittable multi-component fiber of good splittability favorable for use in the field of industrial materials for battery separators, wipers, filters, etc., and also in the field of sanitary materials for napkin, etc., and relates to a method for producing it, and a fibrous article comprising it.
Heretofore known is a method of using sea-island or splittable multi-component fibers for producing fine fibers. In the method of using sea-island multi-component fibers, a plurality of different components are combined and spun into multi-component fibers, and one component of the resulting multi-component fibers is dissolved and removed to give fine fibers. The method gives extremely fine fibers, but is uneconomical as requiring the step of dissolving and removing one component of the multi-component fibers. In the other method of using splittable multi-component fibers, a plurality of different resins are combined and spun into multi-component fibers, and the resulting multi-component fibers are split into a large number of fine fibers by applying physical stress to them or by processing them with a chemical reagent with which the resins constituting each fiber shrink to different degrees. Known are various types of multi-component fibers made from a plurality of different resins, including, for example, a combination of a polyester resin and a polyolefin resin, a combination of a polyester resin and a polyamide resin, a combination of a polyamide resin and a polyolefin resin, etc. However, in the process of splitting the splittable multi-component fibers into fine fibers followed by further processing the resulting fine fibers to give non-woven fabrics and others, the step of splitting the multi-component fibers into fine fibers by processing them with high-pressure liquid jets takes a lot of time, and this is the rate-determining step for the subsequent step of processing the resulting fine fibers to give non-woven fabrics. In addition, the energy cost for the step of splitting the multi-component fibers into fine fibers is high. Moreover, the thus split fine fibers and fibrous articles comprising them inevitably contain different types of polymers, and, at present, their applications in the field of industrial materials that are required to be resistant to chemicals are limited.
On the other hand, in splittable multi-component fibers from a combination of a plurality of resins of the same type, for example, from a combination of polyolefin resins, that of polyester resins, or that of polyamide resins or the like, the constituent polymers are more highly miscible with each other, as compared with those in splittable multi-component fibers from a combination of a plurality of different types of resins such as that mentioned above. Therefore, the multi-component fibers of the former type need greater physical impact for splitting them into fine fibers. As a result, the multi-component fibers thus having received such greater physical impact will be split into uneven fibers, some of which are thick but some others are thin. Such uneven fibers are problematic in that non-woven fabrics made from them have a bad uniformity, and the line speed for processing them with high-pressure liquid jets must be significantly lowered. To that effect, the multi-component fibers are problematic and are not satisfactory.
To solve the problem, Japanese Patent Laid-Open No. 28922/1992 discloses a splittable multi-component fiber comprising a plurality of resins of the same type to which is added an organosiloxane or a modified organosiloxane. They say therein that the splittable multi-component fiber, though comprising polymers of the same type, can be readily split into fine fibers. The splittability of the multi-component fiber disclosed could be enhanced in some degree, but the fiber is still problematic in that the strength of fibrous articles (non-woven fabrics, etc.) comprising the split fibers is low and that the secondary workability of the fibrous articles is poor.
We, the present inventors have assiduously studied so as to obtain splittable multi-component fibers free from the prior art problems noted above, and to obtain uniform fibrous articles comprising them. As a result, we have found that a splittable multi-component fiber comprising at least two thermoplastic resin components, in which one thermoplastic resin component is broken to form a partially conjugated part having been broken in the direction of the fiber axis (see FIG. 2) and/or a non-conjugated part (see FIG. 3) around the multi-component fiber, is readily splittable, and that a fibrous article comprising the splittable multi-component fibers has uniformity. We have also found that a splittable multi-component fiber comprising at least two polyolefin resin components and having a hollow with the individual constituent resin components being alternately radially aligned around the hollow in its cross section and with the percentage of its hollowness falling between 5 and 40%xe2x80x94in which the ratio of the mean length, W, of the outer peripheral arc of one constituent resin component to the mean thickness, L, of the component between the end of the hollow and the outer periphery of the fiber, W/L, falls between 0.25 and 2.5xe2x80x94is readily splittable, and that a fibrous article comprising the splittable multi-component fibers has fineness and uniformity. We have still found that a splittable multi-component fiber comprising at least two thermoplastic resin componentsxe2x80x94in which the constituent components are alternately aligned to be adjacent to each other in the direction of the fiber axis in the cross section of the fiber, the cross section is bent, curved or flattened, and the ratio of the major axis, L, of the cross section to the minor axis, W, thereof, L/W falls between 3 and 20xe2x80x94is readily splittable, and that a fibrous article and a piled fibrous article comprising the splittable multi-component fibers has fineness and uniformity. We have still found that a splittable multi-component fiber comprising at least two thermoplastic resin componentsxe2x80x94in which the constituent components are alternately aligned to be adjacent to each other in the direction of the fiber axis in the cross section of the fiber, the cross section is bent, curved or flattened, and the ratio of the major axis, L, of the cross section to the minor axis, W, thereof, L/W falls between 3 and 20xe2x80x94is readily splittable, and that a fibrous article and a laminated fibrous article comprising the splittable multi-component fibers has fineness and uniformity. On the basis of these findings, we have completed the present invention. As is obvious from the above-mentioned description, the object of the invention is to provide a splittable multi-component fiber capable of being readily split into fine fibers, a method for producing it, a fibrous article having uniformity that comprises the fiber, and a product comprising the article.
The invention is composed of a first aspect including the following (1) to (6), a second aspect including the following (7) to (21), a third aspect including the following (22) to (28), and a fourth aspect including the following (29) to (43).
(1). A splittable multi-component fiber comprising thermoplastic resin components (A) and (B) alternately aligned in its cross section, which is characterized in that the component (A) is formed continuously in the direction of the fiber axis, and the component (B) is so randomly formed that some of it is conjugated to the component (A) in the direction of the fiber axis to give a completely conjugated part and some others of it are broken in the direction of the fiber axis to give a partially conjugated part in which the area conjugated to the component (A) is smaller than that in the completely conjugated part and/or a non-conjugated part in which the component (B) is deleted in the direction of the fiber axis and is not conjugated to the component (A).
(2) The splittable multi-component fiber of above (1), wherein the component (B) is a low-density polyethylene resin, the component (A) is a thermoplastic resin except the low-density polyethylene, and the two components (A) and (B) are alternately radially aligned in the cross section of the fiber to have an alternate radial cross-section profile.
(3) The splittable multi-component fiber of any one of above (1) or (2), wherein the component (A) is a polypropylene resin and the component (B) is a low-density polyethylene resin.
(4) The splittable multi-component fiber of any one of above (1) to (3), which has a hollow cross-section profile.
(5) The splittable multi-component fiber of any one of above (1) to (4), which has a cross-section profile of irregular shape.
(6) A fibrous article comprising the splittable multi-component fibers of any one of above (1) to (5).
(7) A splittable multi-component fiber comprising at least two thermoplastic resin components, which is characterized in that the constituent components are alternately aligned to be adjacent to each other in the direction of the fiber axis in the cross section of the fiber, the cross section is bent, curved or flattened, and the ratio of the major axis, L, of the cross section to the minor axis, W, thereof, L/W falls between 3 and 20.
(8) The splittable multi-component fiber of above (7), wherein the ratio of the outer peripheral length, a, of one constituent component to the contact length, b, thereof neighboring to the adjacent component, a/b, in the cross section falls between 0.1 and 2.5.
(9) The splittable multi-component fiber of any one of above (7) or (8), wherein the ratio of the area, S1, surrounded by the bent or curved constituent components in the cross section to the cross-sectional area, S2, of the fiber, S1/S2 falls between 0.2 and 1.0.
(10) The splittable multi-component fiber of any one of above (7) to (9), wherein at least two constituent, thermoplastic resin components all have, after having formed fibers, a melt flow rate falling between 10 and 100 g/10 min, and the ratio of the melt flow rate, MFR-A, of the resin component (component A) having the highest melting point of all the constituent components to the melt flow rate, MFR-B, of the resin component (component B) having the lowest melting point of all, MFR-A/MFR-B falls between 0.1 and 5.
(11) The splittable multi-component fiber of any one of above (7) to (10), wherein the combination of at least two thermoplastic resin components is a combination of a polypropylene resin and a polyethylene resin.
(12) The splittable multi-component fiber of any one of above (7) to (11), which has, before being split, a single fiber fineness falling between 0.5 and 10 dtex, and gives, after having been split, fine fibers having a single fiber fineness of at most 0.5 dtex.
(13) A fibrous article containing at least 30% by weight of the splittable multi-component fibers of any one of above (7) to (12), in which at least 50% of the fibers are split.
(14) The fibrous article of above (13), which is an aggregate of fiber.
(15) The fibrous article of any one of above (13) or (14), which is an aggregate of fiber obtained by spun-bond method.
(16) A laminated fibrous article, which is formed by laminating a sheet onto one or both surfaces of the fibrous article of any one of above (13) to (15).
(17) A laminated fibrous article, which is formed by laminating the fibrous article of any one of above (13) to (15) onto both surfaces of a sheet.
(18) The laminated fibrous article of any one of above (16) or (17), wherein the sheet is at least one selected from non-woven fabrics, films, knitted fabrics and woven fabrics.
(19) An absorbent article comprising the fibrous article of any one of above (13) to (15) or the laminated fibrous article of any one of above (16) to (18).
(20) A wiper comprising the fibrous article of any one of above (13) to (15) or the laminated fibrous article of any one of above (16) to (18).
(21) A battery separator comprising the fibrous article of any one of above (13) to (15) or the laminated fibrous article of any one of above (16) to (18).
(22) A splittable polyolefin multi-component fiber comprising at least two polyolefin resin components and having a hollow in its center, which is characterized in that the individual constituent components are alternately radially aligned around the hollow in its cross section, the percentage of its hollowness falls between 5 and 40%, and the ratio of the mean length, W, of the outer peripheral arc of one constituent resin component to the mean thickness, L, of the component between the end of the hollow and the outer periphery of the fiber, W/L, falls between 0.25 and 2.5.
(23) The splittable polyolefin multi-component fiber of above (22), wherein the cross-section profile of the hollow is so configured that it has at least one curve of which the radius of curvature (xcfx81) is smaller than the radius of the circle having the same area as the cross-sectional area of the hollow.
(24) The splittable polyolefin multi-component fiber of any one of above (22) or (23), wherein at least two constituent polyolefin resin components all have, after having formed fibers, a melt flow rate falling between 10 and 100 g/10 min, and the ratio of the melt flow rate, MFR-A, of the resin component (component A) having the highest melting point of all the constituent components to the melt flow rate, MFR-B, of the resin component (component B) having the lowest melting point of all, MFR-A/MFR-B falls between 0.1 and 5.
(25) The splittable polyolefin multi-component fiber of any one of above (22) to (24), wherein the combination of at least two polyolefin resin components is a combination of a polypropylene resin and a polyethylene resin.
(26) The splittable polyolefin multi-component fiber of any one of above (22) to (24), wherein the combination of at least two polyolefin resin components is a combination of a stereo-specific polystyrene resin and a polypropylene resin.
(27) The splittable polyolefin multi-component fiber of any one of above (22) to (26), which has, before being split, a single fiber fineness falling between 0.6 and 10 dtex, and gives, after having been split, fine fibers having a single fiber fineness of smaller than 0.6 dtex.
(28) A fibrous article containing at least 30% by weight of the splittable polyolefin multi-component fibers of any one of above (22) to (27), in which at least 50% of the fibers are split.
(29) A splittable polyolefin multi-component fiber comprising at least two polyolefin resin components and having a hollow in its center with the individual constituent components being alternately aligned around the hollow in its cross section, which is deformed by external stress to have a flattened cross-section profile to a degree of deformation (minor axis W/major axis L) falling between 0.2 and 0.9 and is so constructed that at least a part of the constituent components are peeled off.
(30) The splittable polyolefin multi-component fiber of above (29), in which the constituent components are peeled off to a degree of at least 10% of their contact interfaces in the cross section of the fiber.
(31) The splittable polyolefin multi-component fiber of any one of above (29) and (30), wherein the constituent components are alternately radially aligned in the cross section of the fiber.
(32) The splittable polyolefin multi-component fiber of any one of above (29) to (31), wherein the combination of at least two polyolefin resin components is a combination of a polypropylene resin and a polyethylene resin.
(33) The splittable polyolefin multi-component fiber of any one of above (29) to (32), which has, before being split, a single fiber fineness falling between 0.6 and 10 dtex, and gives, after having been split, fine fibers having a single fiber fineness of smaller than 0.6 dtex.
(34) A fibrous article containing at least 30% by weight of the splittable multi-component fibers of any one of above (29) to (33), in which at least 50% by weight of the fibers are split.
(35) The fibrous article of above (34), which is an aggregate of fiber.
(36) The fibrous article of any one of above (34) or (35), which is an aggregate of fiber obtained by spun-bond method.
(37) A laminated fibrous article, which is formed by laminating a sheet onto one or both surfaces of the fibrous article of any one of above (34) to (36).
(38) A laminated fibrous article, which is formed by laminating the fibrous article of any one of above (34) to (36) onto both surfaces of a sheet.
(39) The laminated fibrous article of any one of above (37) or (38), wherein the sheet is at least one selected from non-woven fabrics, films, knitted fabrics and woven fabrics.
(40) An absorbent article comprising the fibrous article of any one of above (34) to (36) or the laminated fibrous article of any one of above (37) to (39).
(41) A wiper comprising the fibrous article of any one of above (34) to (36) or the laminated fibrous article of any one of above (37) to (39).
(42) A battery separator comprising the fibrous article of any one of above (34) to (36) or the laminated fibrous article of any one of above (37) to (39).
(43) A method for producing splittable polyolefin multi-component fibers, which comprises deforming hollowed multi-component fibers with at least two polyolefin resin components being alternately aligned in the cross section of each fiber, by compressing or rubbing them to thereby peel off the constituent components in at least a part of their contact area.